As is known in the art, various styles of pump jacks have been used in combination with oil wells for many years and as one possibility employ fluid power operated piston and cylinder assemblies for operating the pump jack. The fluid assemblies assist in operating the reciprocating down hole pump, sucker rod and polish rods. Perhaps the most common and oldest pump-jack system known today incorporates a walking beam type which utilizes counterweights, a gear box and a prime-mover such as a rotary electric motor or an internal combustion motor which will run on various fuel sources. These units are typically costly to purchase, large and heavy to transport, time consuming to set up, mechanically inefficient and draw a significant amount of power. They also have a heavy foot-print which is unacceptable in environmentally sensitive areas.
As is well recognized in the art, the hydraulic pump jack systems are conventionally used on low to medium production wells and unfortunately have low efficiency (approximately 30 percent) and require extensive power. A further limitation is realized in the environmental unfriendliness of such arrangements, namely, oil leaks and misting inter alia.
Another example of a surface pumping system is referred to as a progressive cavity type pump. Such pumps are employed for use in medium to high volume wells and are particularly useful on wells with heavy sand concentrations or those which are used to produce heavy oil. It has been realized that progressive cavity pumps are not as useful in wells with high hydrogen sulfide concentration or wells containing high concentrations of carbon dioxide. Accordingly, these pumping systems are limited in durability. Another form of a pump jack is a Roto-Flex system. These arrangements have good power efficiency of between 40 and 50 percent and are used in medium to high volume wells and provide for a long stroke capability. Although useful, the Roto-Flex units are not particularly environmentally friendly.
Yet another variation on the pumping arrangements used in fluid extraction includes the electric submersible type pumping units which are particularly useful for large volume wells with no gas. These arrangements are useful in some situations, but are quite limited in environments where wells contain gas in fluid. They also suffer from significant power consumption and poor performance in heavy oil.
In terms of hydraulic/pneumatic pump jack systems which are generally surface based, these have the advantage of being relatively inexpensive to setup and can be customized by the user. Such arrangements are only useful for low to medium volume wells and produce medium efficiency. However, although there are advantages to such arrangements these types of pump jacks perform poorly in very hot weather, very cold weather and are environmentally unfriendly.
A further variation on a pumping system is the conventional “gas lift” system used for removing fluid from a well. These devices require no power and are relatively inexpensive to install and are useful in low volume marginal wells using well gas as the prime mover.
One arrangement known in the art is shown in U.S. Pat. No. 4,201,115, issued May 6, 1980 to Ogles. The system is an oil well pump jack with dual hydraulic operating cylinders. The arrangement incorporates the cylinders for pivoting the walking beam of the jack and includes a unique control arrangement for controlling operating of the piston and cylinders. The control system also permits operation of the hydraulic piston and cylinder assemblies in a double action mode or a single action mode.
Saruwatari, in U.S. Pat. No. 4,114,375, issued Sep. 19, 1978, discloses a pump jack device having a double acting piston and cylinder motor with the piston rod of the motor adapted for connection to the polished rod projecting upwardly from the well head.
In U.S. Pat. No. 4,463,828, issued to Anderson, Aug. 7, 1984, a pump jack is disclosed having a spring handle for cranking the pump jack down and provides a safety lock against accidental unwinding of a helical rod holding the jack on the pole.
Although the devices previously proposed in the art have merit, it is clear that many of the systems employ hydraulically operated cylinders or gear boxes and motors for actuating the reciprocating pump and other critical components in the well. It would be more desirable to have a high efficiency arrangement which did not suffer from the limitations inherent in these systems. The present invention is directed to alleviating the previous limitations in the art.
The present invention discussed in greater detail hereinafter virtually eliminates all the problems with prior art conventional crank and hydraulic surface drive and various other pumping systems. This invention results in a surface drive mechanism that is efficient, both in energy used and oil pumped and also limits the stresses on all the surface and downhole mechanical components. The unit requires very little site preparation, is light weight, easy to move, and simple to install. Conveniently, operation is fully computerized and will act as a “smart” pump jack aiding in the optimization of each specific given well.